It is known in the art that incorporating additives to plastics systems improve characteristics such as tensile strength, flexural strength, elongation or stretching, impact strength, and the like. Many thermoplastics, polyamides (nylons) in particular, are known to be moisture sensitive and will hydrolyze. Therefore, commercially anhydrous fillers are added to such resin systems.
The preparation and subsequent utilization of minerals such as treated clay products as functional fillers for many different resin applications are well known to those skilled in the art. The final end-use applications for such filler products can range from rubber and plastics compounds (both thermoplastic and thermoset types) to uses in industrial coatings, caulks, sealants and adhesives. Several examples of treated calcined clays being used in filler type applications can be found in the patent literature.
U.S. Pat. No. 5,244,958 (1993), describes the preparation of treated calcined clay products particularly useful as fillers in EPDM rubber insulation compounds. Useful calcined clay surface treatments included substituted silanes (e.g., those containing mercapto, amino, vinyl or alkyl type functionality), silazanes, polysiloxanes or select organometallic coupling agents (like organozirconates, organotitanates, etc.).
U.S. Pat. No. 4,740,538 (1988), describes a treated calcined clay useful for nylon plastics whose surface treatment is a dual component system composed of an amino functional silane coupling agent and a triethanolamine or phenol impact modifier. The treated products of this invention are prepared by applying successive chemical surface treatments, i.e. a coating of impact modifier is subsequently coated with a deposit of aminosilane coupling agent.
U.S. Pat. Nos. 4,467,057 (1984) and 4,280,949 (1981), describe the use of a silane-treated calcined clay in conjunction with a polymeric modifier additive to provide increased physical properties to articles molded from polyester compositions.
U.S. Pat. No. 4,427,452 (1984), describes the use of a silane treated, flash-calcined kaolin clay as a functional filler in various elastomeric compositions. Substituted silane coupling agents containing either amino or mercapto type functionality are employed.
U.S. Pat. No. 4,399,246 (1983), describes polyamide compositions containing a mineral filler (such as calcined clay or talc) together with low addition levels of an aminosilane and an N-substituted hydrocarbyl sulfonamide (both chemical additives being added "in situ") to provide molded plastic parts with improved impact resistance.
U.S. Pat. No. 4,357,271 (1982), describes a polycarbonate molding composition containing a calcined clay filler which was pre-treated with aminosilane coupling agent. U.S. Pat. No. 4,235,835 (1980), describes a thermoset ethylene-vinyl acetate composition containing a vinylsilane-treated calcined clay as a functional filler. U.S. Pat. No. 5,260,348 (1993), describes an improved, curable silicone-based composition containing a mineral filler, a cross-linking agent (e.g., an alkyl triacetoxysilane), some adhesion promoter (e.g., an epoxy or an amino functional silane) plus other various components. U.S. Pat. No. 4,179,537 (1979), describes a dual component treatment system for inorganic fillers that improves the adhesion of glass to unsaturated thermoset resins. The preferred surface treatment used on glass consists of a blend of methacryl functional silane and an alkylsilane. U.S. Pat. No. 3,702,783 (1972), describes the treatment of glass filler with a prescribed mixture of epoxysilane and methylsilane to improve its bonding to organic resins like polyamides.
While the treated calcined clay products described above are certainly related scientific art to the treated products of the present invention, none of them teach the use of a silane treatment mixture for minerals such as calcined clays comprising a unique blend of amino functional silane and an alkylsilane which together substantially improve the drop weight impact properties of resin systems and especially of highly filled polyamide compositions. For example, U.S. Pat. Nos. 4,399,246 and 4,740,538 both describe specific chemical additives used in combination with an aminosilane coupling agent to improve the impact properties of filled polyamide compositions. However, neither technology uses a second type of organosilane for this purpose. Furthermore, the first approach involves indirect treatment via the "in situ" addition of both chemical reagents during compounding of the nylon or polyamide composition while the latter approach requires successive clay treatment steps rather than the simultaneous silane treatment approach used in this invention.
It is also known that while the addition of silane treated calcined clays in the appropriate amounts will improve tensile strength and flexural strength of polyamides, they will also decrease the impact strength of the polyamides. Therefore, a continuing problem in the art is to provide the required improvements in other characteristics of the polyamides without adversely affecting the impact strength of the polyamide.